A subdomain is basically a child domain under a larger parent domain name. In the larger scheme of the Domain Name System, it is considered a third-level domain used to organize site content. In the Web address example above (gallery.mysite.com), the suffix ".com" is the first-level domain, "mysite" is the second-level domain and "gallery" is the third-level domain.

Uses of subdomains include:

- Organizing website content according to category, i.e., gallery.mysite.com, faq.mysite.com and store.mysite.com
- Sharing the allotted domain space with other users by providing them subdomains and their own username and password with varying levels of feature access. For example, admin.mysite.com, user1.mysite.com and guest.mysite.com
- Shortening long links and making them easy to remember. For example, the link "http://mysite.com/offers/bonus/referal_id^56$#9?.asp" can be placed into the subdomain "referral.mysite.com" to make it easier to navigate and remember.